Solving the euations we get the coordinates of the quadrilateral.
Slope of = 1
Slope of CD = 1
Slope of BD = AC = - 1
So they form a rectangle with all sides = 90
The quadrilateral is cyclic as sum of opposite angles = 180.
Now, AD = diameter of the circle equation of the circle with extremities A(0, 0)&D(6, - 4) is
(x - 0)(x - 6) + (y - 0)(y + 4) = 0
x2 + y2 – 6x + 4y = 0
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